Casing cutter



Feb. 8, 1966 w. T. BELL 3,233,688

CASING CUTTER Filed Sept. 12, 1965 W////0/77 7 .Be

INVENTOR.

is the casing of the well.

United States Patent 3,233,688 CASING CUTTER William T. Bell, Houston, Tex., assignor to Schlumberger Well Surveying Corporation, Houston, Tex., a corporation of Texas Filed Sept. 12, 1963, Ser. No. 308,386 2 Claims. (Cl. 1754.6)

This invention relates to apparatus for cutting casing and more particularly to an apparatus having a shaped charge portion for cutting casing which lines as well bore.

It is sometimes found necessary in oil field operations to abandon a well for economic reasons. In such a situation it is desirable to salvage as much equipment used in the completion of the well as possible. One such piece of equipment which is often found economical to recover This casing is normally cemented into the well bore with cement extending from a point below to well above the producing zone. In order to recover as much of the casing as possible, special tools have been developed to lower into the well bore and determine where the cement top is located. One method of making this determination utilizes stretching of the casing and locating the cement top by use-of special electronic equipment. When the cement top has been determined, a casing cutter is lowered into the well bore to a point above the cement top and the casing is severed, to subsequently be pulled out of the well bore and reused.

Casing cutters also find use in drilling or completion operations when the drill string becomes stuck. In such situations the drill string is cut above the free point or bridge and removed from the well bore.

Since the casing cutters which contain an explosive charge are normally completely disintegrated and expended in the well bore, it is desirable to provide a cutter which will disintegrate into debris which is small in size the well bore.

Another object of the present invention is to provide a casing cutter construction with interchangeable parts which can be easily assembled.

Still another object of this invention is to provide an explosive charge apparatus for cutting casing. which has a simple and reliable arming operation, leaves a minimum of debris, and which minimizes damage to adjacent parts in the well bore upon detonation.

With these and other objects in view, the present in vention contemplates an explosive charge apparatus for severing casing in a well bore. More particularly, the apparatus includes an annular ring or shell, and mirror image cutter sub-assemblies which are press-fitted into each end of an annular ring or shell and held in such assembled lit by sealing members provided in the sub-assemblies. The sub-assemblies also contain an explosive charge which generates a cutting jet and air spaces positioned above and below the explosive charge to minimize the effects of the explosive force on adjacent parts in the well bore. Additionally, provisions are made for threading a detonating cord all the way through the assemblies to ensure that V the cord adjoins the charge.

A complete understanding of this invention maybe had by reference to the following detailed description when read in conjunction with the accompanying drawings illustrating an embodiment thereof, wherein:

FIG. 1 is a side elevation view of the casing cutter embodying the invention and showing the cutter suspended from a shooting mandrel;

FIG. 2 is a sectional view along the line 22 of FIG. 1.

Referring first to FIG. 1, a shooting mandrel 1 1 which may be suspended in any manner into the well bore is shown having a threaded portion 12 extending therefrom and a bore 15 formed therein. The threaded potrion 12 of the shooting mandrel provides an attaching means for the upper section or upper sub-assembly of the casing cutter. The upper sub-assembly 13 and lower sub-assembly 14 are made up of identical or miror image components and are held together by a cylindrical shell or annular ring member 16 into which the upper and lower sub-assemblies are fitted. The boundary between the upper and lower sub-assemblies is defined by the line 22, therefore, FIG. 2 represents a top view of the lower sub-assembly as it is assembled in the cutter shown in FIG. 1. Since the upper and lower sub assem-blies are identical in design only one will be described in detail.

Each sub-assembly includes a head 21, plate 36, explosive 46 and liner 48. The head 21 has a circular disclike shape and an outer, upper surface formed by an annular peripheral fiat portion 22, a central outwardly extending and internally threaded stub portion 23, and an intermediate dome shaped portion 24. An inner, lower surface of the head 21 is formed by an inwardly extending stub portion 26, a lower annular peripheral fiat portion 27, and an intermediate, semi-circular, annular recess 28, the stub portion 26 and lower flat portion 27 having surfaces lying on a common plane. A circumferental flange 29 extends radially around the head above a cylindrical surface 3-1 grooved to receive on O-ring 32. A bore 33 extends through the stub portions 23 and 26 to interconnect the top and bottom of the head, the bore having outwardly extending beveled edges.

The plate 36 is disc-like with a diameter equal to the diameter of the cylindrical surface 31 on the head. The plate 36 has an upper flat surface 37 to engage thelower peripheral flat portion 27 and the stub portion 26 of the head 21. A lower surface of the plate has an annular recessed flat surface 38 intermediate of a peripheral rim 39 and a central, frusto-conical surface 41, the frustoconical surface adjoining the intermediate flat surface 38. A central bore 42 (also having an upper beveled edge) extends through the plate 36. The explosive 46 is formed on the plate 36 to conform to the lower surface of the plate and has a lateral, frusto-conical surface 47 inclined from the ring 39 of the plate toward the center and fitted with a thin-wall metal liner 48. The liner 48 is complementary in shape to the lateral frusto-conical surface 47 formed on the explosive 46. The explosive 46 also includes a central annular primer portion 49 having a central aperture 51. The liner and explosive charge have a lower face 52 formed on a plane along line 2-2 of the drawing parallel to the upper surface 37 of the plate 36.

In the assembly of this apparatus, a pair of mirror image or identical plates 36 containing an explosive 46, liner 47, and booster 49' therein are inserted respectively through the open ends of shell 16, to fit together in a mirror image relation as shown in FIG. 1; or in the alternative, the shaped charge sections may be fitted together ina mirror image relation and then inserted into the shell 16. Next, the upper and lower cutter heads 21 are press-fitted into the open ends of the shell 16 with the convex or dome shaped side facing outwardly, the bottom side of the circumferential flange 29 receiving the top edge of the cylindrical shell 16, and the lower flat portion 27 and stub 26 abutting the upper surface 37 of the plate 36. The cylindrical surface 31 formed on the outer peripheral wall of the head 21 is received in a press-fit into the inner cylindrical wall of the shell 16. The O-ring 32 positioned in the groove in the cylindrical wall 31 is compressed upon fitting the head 21 into the shell 16 to provide a push-fit between the head 21 and the shell 16 and thereby further hold the parts in assembly. When the cutter assembly is lowered into a Well bore, any fluid present in the well bore will also tend to hold the assembled parts together. It might also be pointed out that other methods of securing the heads in assembly with the shell might be utilized to add an additional safety factor to the assembly. Such means could include screws, adhesive,- or press-fit pins.

After these sub-assemblies are assembled together in the shell 16, the bores 33 in the heads and bores 42 in the plates are now axially aligned with one another and with the aperture 51 formed in the explosive booster 49. Upon completion of the assembly of the abovedescribed parts into a cutter assembly, the apparatus is now ready to be assembled onto the shooting mandrel 11. An internally threaded portion 53 of the outwardly extending stub portion 23 is arranged to receive the threaded portion 12 of the shooting mandrel 11. When used as a lower assembly, the internally threaded portion 53 sealingly receives a plug 55. The plug 55 has a hollow portion 56 formed therein and is assembled in the threaded portion 53 for purposes to be hereinafter described. Therefore, it may be seen that the bore portions 33, 42 and 51, respectively, form a bore extending from the hollow portion 56 in the plug 55 through the cutter assembly to an axial bore 58 in the shooting mandrel 11 which in turn communicates with an enlarged bore 15 in the mandrel thereby providing a communicating passage from the enlarged bore 15 through the entire cutter assembly.

To arm the cutter apparatus, a detonating cord 61 which extends from a blasting cap 62 positioned in the enlarged bore 15 is threaded through the bores 58, 33, 42 and 51 formed in the assembled parts until the loose end of the detonating cord extends through the lower head into the lower cup-shaped portion 53. Beveled edges are formed on each of the bore portions to assist in threading the detonating cord through the assembled parts. A retainer cap 63 is then secured in any wellknown manner, such as by crimping, to the end of the etonating cord to prevent the detonating cord from pulling back through the bores of the assembly. The plug 55, with its hollow portion 56 receiving the cap 63, is then screwed into the internally threaded portion 53 of the lower assembly head to complete the assembly and arming of the casing cutter. The above arming procedure is unique in that the detonating cord 61 is assured of adjoining the booster charge portion 49 since the cord 61 must extend all the way through the assembly before being capped.

In the design of the cutter components, the heads and plates housing the shaped charges, are preferably made of a graphitized light weight, fluid tight, cast iron, such as that sold under the trademark Meehanite. More particularly, a Meehanite type GM is preferably used, this type having the properties of high compressive strength; high tensile strength; dense, fine grain structure; and a low ductility or brittleness. This material meets the requirements outlined in the following specifications: ASTM A48-56 Class 5060, ASTM A278-56 Class 60, and Federal QQ1652a Class 5060. The high compressive and tensile properties render the cutter assembly structurally sound when subjected to the pressures generally encountered in a well bore and the low ductility and fine grain structure properties render the cutter frangible when subjected to an explosive attack so that the assembly disintegrates into small pieces which may be easily drilled through or circulated from the well. The air spaces 28 provided in the heads 21 are semi-circular shaped to provide for ease of casting to conform to the overall low cost design of the casing cutter.

In the operation of this device the blasting cap 62 is ex ploded by a firing circuit connected to the cap, the circuit being energized by any well-known electrical firing means controlled from the surface. Detonation of the blasting cap subsequently fires the detonating cord 61 which in turn detonates the primer or booster 49. The booster explosion wave travels radially outwardly through the booster 49 to detonate the main charge 46. The charge detonates radially outwardly in a symmetrical pattern and the liner 48 forms a cutting jet. The space between the liner and the shell 16, being at atmospheric pressure, permits full development of the jet before it exits through the shell and continues outwardly to cut the casing wall surrounding the cutter.

As the resultant forces generated by the explosive charge which do not form a part of the cutting jet, radiate from the exploding charge, they are transfer-red through the Meehanite plate 36, the air space 28, and the cutter head 21 also made of the Meehanite material. This material is of such a frangible composition that this residual force formed by the exploding shaped charge disintegrates the Meehanite portions of the assembly into small pieces. The air space 28 is of such proportion between the liner and booster to attenuate and dissipate the major energies above that required to shatter the cutter assembly into finely divided portions, thereby preventing damage to other tool parts suspended in the well bore. The air pockets or chambers 28, besides minimizing the shock load on the tool string itself through attenuation of the explosive force in the pockets, also minimize the bomb effect of the radiating explosive charge thereby reducing the splitting and flaring of the cut being made in the easing wall.

While a particular embodiment of the present invention has been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. In a casing cutter for suspension in a well bore;

an externally threaded shooting mandrel;

a tubular, thin-walled shell;

a pair of mirror image housings constructed of frangible material circular shaped charge explosive portions and liner means extending around the periphery of said shaped charge portions attached to said housings,

said housings being shaped for reception in the open ends of said tubular shell with said shaped charge portions abutting to form annular shaped charge means;

a pair of identical domed heads constructed of frangible material and having outer convex walls, peripheral wall portions shaped for reception within said shell and internally-threaded portions formed in the c nvex walls of said domed heads,

said heads having flange portions extending radially from the peripheral wall of said heads defining the upper limit of said peripheral wall portions; seal means fitted into and extending from said peripheral wall adjacent said flange portions,

said heads and housings having bore means aligned for receiving a detonating cord when said heads are fitted into the ends of said shell with the convex walls of said heads facing away from each other, and

an externally threaded plug for assembling into one of said internally-threaded head portions leaving the internally-threaded portion in the other head for threada-bly receiving the externally threaded shooting mam drel.

2. In a casing cutter for suspension in a well bore:

a shooting mandrel;

a tubular thin-walled shell;

a pair of mirror-image housings constructed of frangible material;

circular shaped-charge explosive portions and liner:

means extending around the periphery of said shaped charge portions attached to said housings,

said housings being shaped for reception in the open ends of said cylindrical shell With said shaped charge portions abuttin to form annular shaped charge means;

a pair of identical domed heads constructed of frangible material, each of said heads having an outer convex wall and an inner concave wall, a peripheral wall portion shaped for reception Within said shell and coupling means on the convex walls;

said heads having peripheral flange portions extending therefrom and defining the upper limit of said peripheral wall portions;

seal means around each of said peripheral wall portions;

said heads and housings having bore means aligned for receiving a detonating cord when said heads are fitted into the ends of said shell with the convex walls of Said heads facing away from each other; and

6 closure means coupled to the coupling means of one of said heads for closing one end of said bore means thereby leaving the other of said coupling means on the other of said heads for coupling to said shooting mandrel.

References Cited by the Examiner UNITED STATES PATENTS 2,684,030 7/1954 Muskat et al. 102 2O 2,737,115 3/1956 Bissell 102- 20 2,761,384 9/1956 Sweetman. 2,831,429 4/1958 Moore. 3,057,259 10/ 1962 Christopher.

FOREIGN PATENTS 900,201 11/ 1953 Germany.

BENJAMIN A. BORCH'ELT, Primary Examiner.

SAMUEL FEINBERG. Examiner. 

2. IN A CASING CUTTER FOR SUSPENSION IN A WELL BORE: A SHOOTING MANDREL; A TUBULAR THIN-WALLED SHELL; A PAIR OF MIRROR-IMAGE HOUSINGS CONSTRUCTED OF FRANGIBLE MATERIAL; CIRCULAR SHAPED-CHARGE EXPLOSIVE PORTIONS AND LINER MEANS EXTENDING AROUND THE PERIPHERY OF SAID SHAPED CHARGE PORTIONS ATTACHED TO SAID HOUSING, SAID HOUSINGS BEING SHAPED FOR RECEPTION IN THE OPEN ENDS OF SAID CYLINDRICAL SHELL WITH SAID SHAPED CHARGE PORTIONS ABUTTING TO FORM ANNULAR SHAPED CHARGE MEANS; A PAIR OF IDENTICAL DOMED HEADS CONSTRUTED OF FRANGIBLE MATERIAL, EACH OF SAID HEADS HAVING AN OUTER CONVEX WALL AND AN INNER CONCAVE WALL, A PERIPHERAL WALL PORTION SHAPED FOR RECEPTION WITHIN SAID SHELL AND COUPLING MEANS ON THE CONVEX WALLS; SAID HEADS HAVING PERIPHERAL FLANGE PORTIONS EXTENDING THEREFROM AND DEFINING THE UPPER LIMIT OF SAID PERIPHERAL WALL PORTIONS; SEAL MEANS AROUND EACH OF SAID PERIPHERAL WALL PORTIONS; SAID HEADS AND HOUSINGS HAVING BORE MEANS ALIGNED FOR RECEIVING A DETONATING CORD WHEN SAID HEADS ARE FITTED INTO THE ENDS OF SAID SHELL WITH THE CONVEX WALLS OF SAID HEADS FACING AWAY FROM EACH OTHER; AND CLOSURE MEANS COUPLED TO THE COUPLING MEANS OF ONE OF SAID HEADS FOR CLOSING ONE END OF SAID BORE MEANS THEREBY LEAVING THE OTHER OF SAID COUPLING MEANS ON THE OTHER OF SAID HEADS FOR COUPLING TO SAID SHOOTING MANDREL. 